This invention relates to joining metal members together, and more particularly to joining methods which employ adhesives and which provide enhanced thermal conductivity between the joined members.
When metal parts are to be joined together, spot welding or fasteners may produce a cheaper but weaker joint than brazing, soldering or adhesives. Brazing and soldering provide a strong joint with good heat transfer properties because the joint is occupied by thermally conductive metal. The fastener or spot welded joint provides poor thermal contact between the parts except at isolated points. Various thermally conductive adhesive formulations are available for metals, but their conductivity is so much less than the metals they are joining that the joint provides a serious barrier to the transfer of heat between metal parts thus joined. For example, a typical joint formed with a thermally conductive epoxy adhesive between aluminum parts is the thermal conductivity equivalent of a thickness of 8.9 millimeters of aluminum even though it is only a fraction of a millimeter thick. This is a joint formed with an alumina filled epoxy using the recomended 15 P.S.I. or 1.05 Kg/cm.sup.2 clamping force. In the fabrication of many devices such as heat exchangers, such a serious impediment to heat transfer may prevent the use of adhesives. Consequently, brazing and soldering are preferred, even though they may be very costly to implement, being labor intensive and requiring special fixtures, and warping considerations.